The present invention relates to a heat treating device, such as a vertical CVD device.
Heat treating devices are generally used as devices for conducting required heat treatments on objects to be treated, such as semiconductor wafers, in uniform temperature states, for forming thin films on the surfaces of the objects and for carrying out thermal diffusion thereon.
FIG. 9 is a vertical sectional view of one example of the conventional vertical heat treating devices. A heat treatment furnace 2 comprises a processing vessel 8 including an inner tube 4 of quartz having the top and the bottom opened, and an outer tube 6 of quartz concentrically spaced from the outer circumference of the inner tube by a set distance, and having a ceiling 6A and an opened bottom. A heater (not shown) is disposed around the outer circumference of the processing vessel 8.
The inner and the outer tubes 4, 6 have respective lower ends supported by a manifold 10 of, stainless steel. Processing gas feed nozzles 12 for introducing processing gases are horizontally inserted into the interior of the manifold 10, and an exhaust pipe 14 is connected to the manifold 10 for evacuating the interior of the processing vessel 8. The processing gas introduced into the processing vessel 8 ascends in the inner tube 4 and descends between the inner and the outer tubes 4, 6 to be discharged outside through the exhaust pipe 14.
A wafer boat 16 with a number of semiconductor wafers W as objects to be treated mounted horizontally spaced from each other in the longitudinal direction of the wafer boat of, e.g., quartz is loaded into the inner tube 4. The wafer boat 16 is placed on the top of a heat retention cylinder 18 of quartz having the interior filled with heat insulating glass wool.
The lower end opening of the manifold 10 is openably made air-tight by a disk-shaped cap 20 through an O-ring 22. The cap 20 is supported on a rotary shaft 28 provided on an arm 26 of lift means 24, such as an elevator, through a magnetic seal 30. A ring 32 for receiving the heat retention cylinder 18 is secured to the upper end of the rotary shaft 28, and the above-mentioned heat retention cylinder 18 is provided on the rotary shaft 28. The rotary shaft 28 is rotated through a pulley 34 by a power belt 36 of a motor (not shown).
During heat treatment of the objects to be treated, the rotary shaft 28 is rotated by the motor to rotate the wafers W on the wafer boat 16 while the wafers W are being exposed to ascending processing gases, whereby intra-plane uniformity of deposited films on the surfaces of the wafers can be made as high as possible.
When the wafers W are loaded into/unloaded out of the processing vessel 8, the lift means 24 is driven to move up together the cap 20, the heat retention cylinder 18 and the wafer boat 16 to load/unload the wafers into/out of the processing vessel 8.
In the devices of the above-described conventional structure, the wafer boat 16 of FIG. 9 has to be rotated during a heat treatment so as to secure uniform heating, specifically intra-plane uniformity of, e.g, a deposition, especially uniform treatment between those of the wafers loaded at the central parts of the wafer boat and those at the bottom thereof. To this end, a rotary mechanism is needed, and because heat treatments are conducted in vacuum states, the magnetic seal 30 which functions, while securing the seal, as the bearing for permitting the rotation of the rotary mechanism has to be used. This makes the structure more complicated, which is a factor for high costs. This is one problem with the conventional heat treating devices.
Furthermore, because magnetic fluid used in the magnetic seal 30 is relatively vulnerable to heat, it is necessary to provide a water cooling pipe or other means (not shown) in the arm 26 of the elevator 24 to cool the magnetic seal 30. This makes the structure more complicated, which is a factor for high costs.
The cooling pipe or other means cools the surrounding of the cap 20 containing the magnetic seal 30 to a lower temperature relative to the other parts, and depositions of the processing gases tend form on the surrounding. The depositions peel off and float as particles, which contaminate the wafers. This is also a problem.
Furthermore, although the magnetic fluid used in the magnetic seal 30 is cooled, the magnetic fluid reacts with the processing gases, and its sealing ability is gradually degraded. A resultant problem is the magnetic fluid leaks from the magnetic seal 30. Maintenance inspection thereof is needed every 3 to 6 months.